The Real name is Biohazard not Resident Evil. Biohazard is better known in Japan but it was renamed as Resident Evil for western release in order to avoid copyright issues.

Resident Evil was inspired by a classic game named Sweet Home that was released for the Famicom in 1989.

Resident Evil 2 and 4 were rebuild from the ground up. They are videos of RE 2 and 4 prototypes, labeled as 1.5 and 3.5. both of them show how the games were supposed to look like, but the developers were unhappy with the result so they took the risk of developing the game again from scratch. It happened to RE 1.5(2) and RE 3.5(4)

(Resident Evil 1.2 is leaked and it's playable)

Devil May Cry started as a Resident Evil game. Dante was supposed to be the protagonist of Resident Evil 4. Developers found the character doesn't fit but it's too good to be abandoned, so they decide for Dante to have his own series, so Devil My Cry was born.

There's a Resident Evil Joke/Internet Meme known as Jill Sandwich. In the Resident Evil 1, there's a scene where Barry Burton saves Jill Valentine from descending ceiling trap that meant to squash her, he makes a humorous joke and says "That was too close; you were almost a Jill sandwich"